Allocation of the same IP in DHCP that is busy.

DienoX

Hello
I have a question that has been interesting to me for a long time.
How pfsense will behave in this situation:
I have configured a manual configuration of a NIC without DHCP in a DHCP pool. In that case, will pfsense allocate same address from DHCP to another device? I am talking of course about the situation without DHCP reservation.

I would like to ask you for a short answer and a long one, because this topic interests me very much.

JKnott

@dienox

Why does this sound like a homework question?

One method that's often used to check is something called duplicate address detection. It's mandatory with IPv6 but can also be used with IPv4.

noplan

@jknott said in Allocation of the same IP in DHCP that is busy.:

homework question

the short answer is never do it
Most of the dhcp servers out there will assign the ip to a request and then u ll get duplicated IPs

That's also the reason why static mapping in dhcp always should be outside the dhcp pool

DienoX

The topic applies to home and corporate networks. I am asking in the context of the DHCP server in the pfsense system. I just need to know what DHCP will do in the case of the first post.

noplan

@dienox

assign the next free address out of the pool

if you set it as fixed IP on the client, how tha hack should pfS dhcp gonna konw that this specific IP (you set as fix IP on the client) in its DHCP range is not allowed to be handed out from the pool.

if u r in a corporate env, u r facing troubles !
have a nice day

JKnott

@dienox said in Allocation of the same IP in DHCP that is busy.:

The topic applies to home and corporate networks. I am asking in the context of the DHCP server in the pfsense system. I just need to know what DHCP will do in the case of the first post.

You should never manually configure an address within the DHCP pool. As I mentioned, DAD may help, but if it happens, you will have a conflict, with one device or the other claiming the address. There will be error messages when that happens. Why not give it a try and see what happens. Run Wireshark or Packet Capture to see what happens.